U.S. patent number 8,420,879 [Application Number 13/411,080] was granted by the patent office on 2013-04-16 for process for workup of a stream comprising butene and/or butadiene.
This patent grant is currently assigned to BASF SE. The grantee listed for this patent is Regina Benfer, Jochen Gotz, Grigorios Kolios, Albena Kostova, Aristides Morillo, Gerhard Olbert, Peter Pfab, Alireza Rezai, Markus Weber, Alexander Weck. Invention is credited to Regina Benfer, Jochen Gotz, Grigorios Kolios, Albena Kostova, Aristides Morillo, Gerhard Olbert, Peter Pfab, Alireza Rezai, Markus Weber, Alexander Weck.
United States Patent |
8,420,879 |
Kostova , et al. |
April 16, 2013 |
Process for workup of a stream comprising butene and/or
butadiene
Abstract
The invention relates to a process for workup of a stream (1)
comprising butene and/or butadiene, butane, hydrogen and/or
nitrogen and carbon dioxide, comprising: (a) absorption of stream
(1) with a mixture (5) comprising 80 to 97% by weight of
N-methylpyrrolidone and 3 to 20% by weight of water to obtain a
stream (9) comprising N-methylpyrrolidone, water, butene and/or
butadiene, butane, and optionally carbon dioxide, and a stream (7)
comprising hydrogen and/or nitrogen and butane, (b) extractive
distillation of stream (9) with a stream (13) comprising 80 to 97%
by weight of N-methylpyrrolidone and 3 to 20% by weight of water to
separate the stream (9) into a stream (17) comprising
N-methylpyrrolidone, water, butene and/or butadiene, and a stream
(15) comprising essentially butane, and optionally carbon dioxide,
(c) distillation of stream (17) into a stream (23) comprising
essentially N-methylpyrrolidone and water, and a stream (21)
comprising butene and/or butadiene.
Inventors: |
Kostova; Albena (Mannheim,
DE), Benfer; Regina (Altrip, DE), Gotz;
Jochen (Speyer, DE), Rezai; Alireza (Mannheim,
DE), Morillo; Aristides (Katy, TX), Olbert;
Gerhard (Dossenheim, DE), Pfab; Peter (Shaker
Heights, OH), Kolios; Grigorios (Neustadt, DE),
Weber; Markus (Limburgerhof, DE), Weck; Alexander
(Freinsheim, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kostova; Albena
Benfer; Regina
Gotz; Jochen
Rezai; Alireza
Morillo; Aristides
Olbert; Gerhard
Pfab; Peter
Kolios; Grigorios
Weber; Markus
Weck; Alexander |
Mannheim
Altrip
Speyer
Mannheim
Katy
Dossenheim
Shaker Heights
Neustadt
Limburgerhof
Freinsheim |
N/A
N/A
N/A
N/A
TX
N/A
OH
N/A
N/A
N/A |
DE
DE
DE
DE
US
DE
US
DE
DE
DE |
|
|
Assignee: |
BASF SE (DE)
|
Family
ID: |
46753715 |
Appl.
No.: |
13/411,080 |
Filed: |
March 2, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20120226087 A1 |
Sep 6, 2012 |
|
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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61448672 |
Mar 3, 2011 |
|
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Current U.S.
Class: |
585/809; 585/860;
585/833; 585/810 |
Current CPC
Class: |
C07C
7/11 (20130101); C07C 7/04 (20130101); C07C
7/08 (20130101); C07C 7/04 (20130101); C07C
11/08 (20130101); C07C 7/04 (20130101); C07C
11/167 (20130101); C07C 7/08 (20130101); C07C
11/167 (20130101); C07C 7/08 (20130101); C07C
11/08 (20130101); C07C 7/11 (20130101); C07C
11/08 (20130101); C07C 7/11 (20130101); C07C
11/167 (20130101) |
Current International
Class: |
C07C
7/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102004059356 |
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Jun 2006 |
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DE |
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102004061514 |
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Jul 2006 |
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DE |
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1682468 |
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Jul 2006 |
|
EP |
|
1159915 |
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Jun 1985 |
|
SU |
|
WO-2006050969 |
|
May 2006 |
|
WO |
|
Other References
US. Appl. No. 12/950,646, filed Nov. 19, 2010, Steiner et al. cited
by applicant .
U.S. Appl. No. 12/957,618, filed Dec. 1, 2010, Kolios et al. cited
by applicant .
U.S. Appl. No. 61/425,280. cited by applicant .
U.S. Appl. No. 61/491,911. cited by applicant.
|
Primary Examiner: Nguyen; Tam M
Attorney, Agent or Firm: Novak Druce Connolly Bove + Quigg
LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
61/448,672, filed Mar. 3, 2011, which is incorporated by reference.
Claims
The invention claimed is:
1. A process for workup of a stream (1) comprising butene and/or
butadiene, butane, hydrogen and/or nitrogen and carbon dioxide,
comprising the following steps: (a) absorption of the stream (1)
with a mixture (5) comprising 80 to 97% by weight of
N-methylpyrrolidone and 3 to 20% by weight of water to obtain a
stream (9) comprising N-methylpyrrolidone, water, butene and/or
butadiene, and butane, with or without carbon dioxide, and a stream
(7) comprising hydrogen and/or nitrogen and butane, (b) extractive
distillation of the stream (9) with a stream (13) comprising 80 to
97% by weight of N-methylpyrrolidone and 3 to 20% by weight of
water to separate the stream (9) into a stream (17) comprising
N-methylpyrrolidone, water, butene and/or butadiene, and a stream
(15) comprising essentially butane, with or without carbon dioxide,
(c) distillation of the stream (17) into a stream (23) comprising
essentially N-methylpyrrolidone and water, and a stream (21)
comprising butene and/or butadiene.
2. The process according to claim 1, wherein the stream (15) is
condensed to remove carbon dioxide.
3. The process according to claim 1, wherein at least a portion of
the stream (23) removed in step (c) is recycled into the absorption
and/or into the extractive distillation.
4. The process according to claim 1, wherein the absorption in step
(a) is performed at a bottom temperature in the range from 30 to
160.degree. C., a top temperature in the range from 5 to 60.degree.
C. and a pressure in the range from 2 to 20 bar.
5. The process according to claim 1, wherein the absorption in step
(a) is performed in a column (3) to which the stream (5) the stream
(1) are added in countercurrent.
6. The process according to claim 1, wherein the extractive
distillation in step (b) is performed in an extractive distillation
column (11) to which the stream (9) and the stream (13) are added
in countercurrent.
7. The process according to claim 1, wherein the stream (7) removed
in the absorption in step (a) is at least partly recycled into a
butane dehydrogenation from which the stream (1) originates.
8. The process according to claim 1, wherein the butane removed in
the extractive distillation in step (b) is recycled into a butane
dehydrogenation.
9. The process according to claim 1, wherein the ratio of mixture
of water and N-methylpyrrolidone added in the absorption in step
(a) to the mixture of water and N-methylpyrrolidone added in the
extractive distillation in step (b) is in the range from 0.2 to 20.
Description
BACKGROUND OF THE INVENTION
The invention relates to a process for workup of a stream
comprising butene and/or butadiene, butane, hydrogen and/or
nitrogen, with or without carbon dioxide.
Butenes and butadiene can be prepared, for example by thermal
cleavage (steam-cracking) of saturated hydrocarbons, typically
proceeding from naphtha as a raw material. The steamcracking of
naphtha gives a hydrocarbon mixture of methane, ethane, ethene,
acetylene, propane, propene, propyne, allene, methylallene, and
C.sub.5 and higher hydrocarbons.
A disadvantage of this process for producing butenes and butadiene
is that relatively large amounts of unwanted coproducts are
inevitably obtained. Alternatively, the butenes can be prepared
from butane and butadiene from n-butene, by dehydrogenation.
DE-A 10 2004 059 356 discloses, for example, preparing butadiene by
using n-butane as a feedstock. To prepare the butadiene, the
n-butane is dehydrogenated in a dehydrogenation zone by
nonoxidative catalytic dehydrogenation to give a stream comprising
n-butane, 1-butene, 2-butene, butadiene, and hydrogen, with or
without carbon dioxide and with or without water vapor. In a second
dehydrogenation zone, the 1-butene and 2-butene are dehydrogenated
further to butadiene. The stream obtained in the dehydrogenation is
subsequently compressed and cooled in order to condense out water.
A product stream comprising essentially butadiene is removed by
extractive distillation from the residual stream comprising
n-butane, butadiene, hydrogen, carbon dioxide and water vapor.
A corresponding process for preparing butadiene from n-butane is
additionally also described in DE-A 10 2004 061 514.
A disadvantage of the process described here is that a different
solvent than in the extractive distillation is used for the removal
of an H.sub.2-rich stream in the absorption, and thus a desorption
stage for the H.sub.2-rich gas is also needed. In addition there is
no separation of CO.sub.2 and H.sub.2.
A further process for workup of a stream comprising butenes is also
known from SU-A 1159915. In this process, the stream comprising
butenes is subjected first to an absorption and then to an
extractive distillation. The solvent used for the absorption and
the extractive distillation is acetonitrile. A disadvantage in the
case of the use of acetonitrile is that it does not dissolve any
carbon dioxide. The use of acetonitrile therefore leads to the
effect that the proportion of carbon dioxide in the gas increases
since the carbon dioxide is recycled into the butane
dehydrogenation together with the hydrogen and is not washed out in
the absorption.
WO-A 2006/050969 describes a process for preparing butadiene from
n-butane, in which the butadiene-comprising stream from the
dehydrogenation is first cooled in order to condense out water. In
a further compression stage and cooling, a condensate stream
comprising n-butane, butadiene and water is obtained. n-Butane and
butadiene are removed from the stream comprising water, n-butane
and butadiene, and then separated into a product stream consisting
essentially of butadiene and a recycle stream comprising
n-butane.
A disadvantage here is that the C.sub.4 components are removed from
the inert gases by a multistage compression and subsequent
condensation. This process stage features a high energy requirement
for the compression up to approx. 30 bar. The C.sub.4 condensation
is effected at a temperature of 10.degree. C., and thus a cooling
unit is additionally required.
A process for preparing 1-butene is described, for example, in EP-B
1 682 468. In the process described here, a C.sub.4 stream is
removed in a two-stage process by absorption and a subsequent
desorption of inerts. A disadvantage of the process is that the
absorption solvent (tetradecane) is different than the solvent used
in the extractive distillation (NMP). Moreover, there is the risk
of mixing of the two solvents, which results in a reduced
selectivity of the absorption and extractive distillation stages. A
further disadvantage here is that the absorbent is selective only
for C.sub.4 and hence there is no removal of H.sub.2 and CO.sub.2.
The use of different solvents in the absorption step entails a
desorption of the C.sub.4 component with steam before it is passed
on into the NMP extractive distillation column.
It is an object of the present invention to provide a process for
workup of a stream comprising butene and/or butadiene, which can be
implemented with less complexity and lower costs.
BRIEF SUMMARY OF THE INVENTION
The object is achieved by a process for workup of a stream
comprising butene and/or butadiene, butane, hydrogen and/or
nitrogen, with or without carbon dioxide, comprising the following
steps: (a) absorption of the stream comprising butene and/or
butadiene, butane, hydrogen and/or nitrogen, with or without carbon
dioxide, with a mixture comprising 80 to 97% by weight of
N-methylpyrrolidone and 3 to 20% by weight of water to obtain a
stream comprising N-methylpyrrolidone, water, butene and/or
butadiene, and butane, with or without carbon dioxide, and a stream
comprising hydrogen and/or nitrogen and butane, (b) extractive
distillation of the stream comprising N-methylpyrrolidone, water,
butene and/or butadiene, and butane, with or without carbon
dioxide, with a stream comprising 80 to 97% by weight of
N-methylpyrrolidone and 3 to 20% by weight of water to separate the
stream comprising N-methylpyrrolidone, water, butene and/or
butadiene, and butane, with or without carbon dioxide, into a
stream comprising N-methylpyrrolidone, water, butene and/or
butadiene, and a stream comprising essentially butane, with or
without carbon dioxide, (c) distillation of the stream comprising
N-methylpyrrolidone, water, butene and/or butadiene into a stream
comprising essentially N-methylpyrrolidone and water, and a stream
comprising butene and/or butadiene.
According to the invention, a mixture of 80 to 97% by weight of
N-methylpyrrolidone and 3 to 20% by weight of water, preferably a
mixture of 90 to 93% by weight of N-methylpyrrolidone and 7 to 10%
by weight of water and especially a mixture of 91 to 92% by weight
of N-methylpyrrolidone and 8 to 9% by weight of water, for example
a mixture of 91.7% by weight of N-methylpyrrolidone and 8.3% by
weight of water, is used both as the solvent for the absorption in
step (a) and as the extractant for the extraction in step (b).
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows a working example of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the invention is notable for particularly
effective removal of the butenes and/or of the butadiene. Thus,
losses resulting from incomplete condensation of the butenes and/or
of the butadiene are minimized. The process according to the
invention proceeds at lower pressures than a C.sub.4 condensation
and does not require low temperatures. The process is thus more
energetically efficient than the processes known from the prior
art. In contrast to absorption/desorption processes followed by an
extractive distillation, the same solvent is used in the process
according to the invention, with a reduction in the number of
columns needed. In addition, it is also impossible for different
solvents to mix.
The use of a mixture of N-methylpyrrolidone and water as a solvent
for the absorption and as an extractant in the extractive
distillation has the advantage that the boiling point is lower than
the boiling point in the case of use of pure N-methylpyrrolidone. A
further advantage is that increasing the water content in the
mixture of water and N-methylpyrrolidone used as the solvent can
enhance the selectivity. However this leads as expected to a
reduction in the capacity. A further advantage is the selectivity
of the N-methylpyrrolidone for carbon dioxide. This enables, in
addition to the removal of the hydrocarbons, a removal of the
carbon dioxide from the hydrogen.
In the context of the present invention, butene is always
understood to mean 1-butene, 2-butene (cis and trans) and
isobutene. In this context, the different butenes may each occur
individually or in any mixtures with one another.
The stream comprising butene and/or butadiene, butane, hydrogen
and/or nitrogen, with or without carbon dioxide, may originate, for
example, from a butane dehydrogenation and/or a butene
dehydrogenation.
A butene-rich stream can arise, for example, as a product stream in
a butane dehydrogenation and comprises generally 20 to 70% by
volume of butane (n-butane, isobutane), 0 to 40% by volume of
isobutene, 1 to 15% by volume of 1-butene, 1 to 25% by volume of
2-butene (cis/trans-butene), 0.1 to 15% by volume of butadiene, 1
to 70% by volume of water vapor, 0.1 to 40% by volume of hydrogen,
0 to 10% by volume of nitrogen, 0 to 10% by volume of low-boiling
hydrocarbons (ethane, ethene, methane, propane, propene) and 0 to
5% by volume of carbon oxides.
The starting material supplied to the butane dehydrogenation is a
use gas stream which comprises generally at least 60% by weight of
butane, preferably at least 90% by weight of butane. In addition,
it may also comprise C.sub.1-C.sub.6 hydrocarbons as secondary
constituents. The butane dehydrogenation can be conducted as a
catalytic non-oxidative or oxidative dehydrogenation. The butane
supplied can be added as n-butane, as isobutane or as a mixture of
n-butane and isobutane. Preference is given to adding n-butane.
In a nonoxidative catalytic dehydrogenation, the butane-comprising
use gas stream is fed into a dehydrogenation zone and subjected to
the nonoxidative catalytic dehydrogenation. This involves partly
dehydrogenating n-butane in a dehydrogenation reactor over a
dehydrogenation-active catalyst to give 1-butene and 2-butene, also
forming butadiene. In addition, hydrogen and small amounts of
methane, ethane, ethene, propane and propene are obtained.
According to the mode of operation of the dehydrogenation, it is
also possible for carbon oxides (carbon monoxide and carbon
dioxide), water and nitrogen to be present in the product gas
mixture of the non-oxidative catalytic n-butane dehydrogenation. In
addition, unconverted butane is present in the product gas mixture
of the nonoxidative catalytic dehydrogenation.
The nonoxidative n-butane dehydrogenation can in principle be
performed in all reactor types and modes of operation known from
the prior art. A comparatively detailed description of suitable
dehydrogenation processes is also present in "Catalytica.RTM.
Studies Division, Oxidative Dehydrogenation and Alternative
Dehydrogenation Processes" (Study No. 412 OD, 1993, 430 Ferguson
Drive, Mountain View, Calif., 94043-5272, USA).
The nonoxidative catalytic butane dehydrogenation can be performed
with or without oxygenous gas as a cofeed. It is preferably
performed as an autothermal non-oxidative dehydrogenation with
supply of oxygen as a co-feed. In the autothermal mode of
operation, the heat required is produced directly in the reactor
system by combustion of hydrogen and/or hydrocarbons in the
presence of oxygen. Optionally, it is additionally possible to add
a hydrogen-comprising co-feed. In at least one reaction zone,
oxygen is additionally added to the reaction gas mixture of the
n-butane dehydrogenation, and the hydrogen and/or hydrocarbon
present in the reaction gas mixture is at least partly combusted,
which generates at least a portion of the heat of dehydrogenation
required in the at least one reaction zone directly in the reaction
gas mixture. Oxygen can be fed in as an oxygen/steam mixture or as
an air/steam mixture. By virtue of the use of an oxygen/steam
mixture, only small amounts of inert gases (nitrogen) are
introduced into the overall process.
In general, the amount of the oxygenous gas added to the reaction
gas mixture is selected such that the combustion of hydrogen
present in the reaction gas mixture and of any hydrocarbons present
in the reaction gas mixture and/or of carbon present in the form of
coke generates the amount of heat required for the dehydrogenation
of the butane. In general, the total amount of oxygen supplied,
based on the total amount of butane, is 0.001 to 0.5 mol/mol,
preferably 0.005 to 0.2 mol/mol, more preferably 0.05 to 0.2
mol/mol.
The hydrogen combusted to generate heat is hydrogen formed in the
catalytic butane dehydrogenation and optionally hydrogen added
additionally as a hydrogenous gas to the reaction gas mixture.
Preferably, a sufficient amount of hydrogen should be present that
the molar H.sub.2/O.sub.2 ratio in the reaction gas mixture
immediately after the feeding of oxygen is 1 to 10, preferably 2 to
5 mol/mol. In the case of multistage reactors, this applies to each
intermediate feeding of oxygenous, and optionally hydrogenous,
gas.
The hydrogen is combusted catalytically. The dehydrogenation
catalyst used generally also catalyzes the combustion of the
hydrocarbons and of hydrogen with oxygen, and so in principle no
specific oxidation catalyst is required. Suitable catalysts are
described, for example, in DE-A 10 2004 061 514.
In one embodiment of the process according to the invention, there
is intermediate feeding of oxygenous gas and hydrogenous gas
upstream of each stage of a staged reactor. In a further embodiment
of the process according to the invention, oxygenous gas and
hydrogenous gas are fed in upstream of every stage except the first
stage. In one embodiment, beyond each feed point, a layer of a
specific oxidation catalyst is present, followed by a layer of the
dehydrogenation catalyst. In a further embodiment, no specific
oxidation catalyst is present. The dehydrogenation temperature is
generally 400 to 1100.degree. C., the pressure in the last catalyst
bed of the staged reactor generally 0.2 to 5 bar, preferably 1 to 3
bar. The space velocity (GHSV) is generally 500 to 2000 h.sup.-1,
and in high-load mode even up to 100 000 h.sup.-1, preferably 4000
to 16 000 h.sup.-1.
The butane dehydrogenation is preferably performed in the presence
of water vapor. The water vapor added serves as a heat carrier and
promotes the gasification of organic deposits on the catalysts,
which counteracts the coking of the catalysts and increases the
service life of the catalysts. This converts the organic deposits
to carbon monoxide, carbon dioxide, and possibly water.
It is a feature of the nonoxidative operating mode compared to an
oxidative operating mode that no free hydrogen is formed in
significant amounts in the oxidative dehydrogenation.
A butadiene-rich stream can be obtained, for example, in a butene
dehydrogenation. In general, the butadiene-rich stream obtained in
the butene dehydrogenation comprises 10 to 40% by volume of
butadiene, 15 to 79.9% by volume of n-butane, 0 to 10% by volume of
2-butene, 0 to 2% by volume of 1-butene, 10 to 70% by volume of
water vapor, 0 to 10% by volume of low-boiling hydrocarbons
(methane, ethane, ethene, propane and propene), 0.1 to 15% by
volume of hydrogen, 0 to 10% by volume of nitrogen, 0 to 15% by
volume of carbon dioxide and 0 to 7% by volume of oxygenates.
Oxygenates may be, for example, furan, acetic acid, maleic
anhydride, maleic acid, propionic acid, acetaldehyde, acrolein,
formaldehyde, formic acid and butyraldehyde. In addition, traces of
acetylene, propyne and 1,2-butadiene may be present.
The butene dehydrogenation can be operated as an individual process
or in combination with a butane dehydrogenation. The butene
dehydrogenation can be operated nonoxidatively or oxidatively (with
an O.sub.2-rich gas as an oxidizing agent).
Preference is given to oxidative butene dehydrogenation. The
oxidative dehydrogenation can in principle be performed in all
reactor types and operating modes known from the prior art, for
example, in a fluidized bed, in a staged oven, in a fixed bed
tubular or tube bundle reactor, or in a plate heat exchanger
reactor. Performance of the oxidative dehydrogenation requires a
gas mixture which has a molar oxygen:n-butenes ratio of at least
0.5. Preference is given to working at an oxygen:n-butenes ratio of
0.55 to 50. To adjust this value, the product gas mixture
originating from the nonoxidative catalytic dehydrogenation is
generally mixed with pure oxygen or an oxygenous gas, directly or
after a workup in which butenes are concentrated and hydrogen is
removed. In one embodiment the oxygenous gas comprises, as in the
case of the first (autothermal) dehydrogenation stage,
predominantly oxygen, at least 75% by volume, preferably at least
90% by volume, in order to minimize the inert gas content in the
product gas stream of the oxydehydrogenation. In this case, oxygen
of technical grade purity is preferred. The resulting oxygenous gas
mixture is then supplied to the oxydehydrogenation. A preferable
alternative to an oxygenous gas comprising at least 75% by volume
of oxygen is to use air or lean air with a proportion of less than
23% by volume as the oxygenous gas.
The oxydehydrogenation is performed generally at a temperature of
220 to 490.degree. C. and preferably of 250 to 450.degree. C. A
reactor inlet pressure sufficient to overcome the flow resistances
present in the plant and the downstream workup is selected. This
reactor inlet pressure is generally 0.005 to 1 MPa gauge,
preferably 0.01 to 0.5 MPa gauge. Naturally, the gas pressure
employed in the inlet region of the reactor declines substantially
over the overall bed of catalyst.
The product gas stream leaving the oxidative dehydrogenation
comprises, as well as butadiene and unconverted n-butane, also
hydrogen, carbon dioxide and water vapor. As secondary constituents
it may also comprise oxygen, nitrogen, methane, ethane, ethene,
propane and propene, and oxygenous hydrocarbons, called oxygenates.
In general, it comprises virtually no 1-butene any longer and only
small proportions of 2-butene.
In a preferred embodiment, water is removed from the product stream
after the dehydrogenation. The water is preferably removed in a
quench.
The stream which comprises butadiene and/or butene, butane,
hydrogen and/or nitrogen, with or without carbon dioxide and which
may originate from an oxydehydrogenation or nonoxidative
dehydrogenation after partial condensation of water vapor, is
supplied as a starting stream to step (a) of the workup.
The absorption in step (a) can be performed in any desired suitable
absorption column known to those skilled in the art. Preference is
given to performing the absorption in countercurrent. For this
purpose, the stream comprising butene and/or butadiene, butane,
hydrogen and/or nitrogen, with or without carbon dioxide, is
supplied to the absorption column in the lower region. In the upper
region of the absorption column, the stream comprising
N-methylpyrrolidone and water is introduced.
At the top of the absorption column, a hydrogen-rich and/or
nitrogen-rich stream is withdrawn, which may also comprise residues
of C.sub.4 hydrocarbons and possibly carbon oxygenates. In
addition, this stream may comprise inerts (for example, nitrogen)
and low boilers (ethane, ethene, propane, propene, methane). The
stream comprising N-methylpyrrolidone and water cools the supplied
stream comprising butene and/or butadiene, butane, hydrogen and/or
nitrogen, with or without carbon dioxide, and at the same time
preferentially absorbs the C.sub.4 components and some CO.sub.2. In
some cases, small amounts of H.sub.2, inerts (N.sub.2) and low
boilers are also absorbed. This stream is drawn off at the bottom
of the absorption column.
The absorption in step (a) is performed generally at a bottom
temperature in the range from 30 to 160.degree. C., a top
temperature in the range from 5 to 60.degree. C., and a pressure in
the range from 2 to 20 bar. Preference is given to performing the
absorption at a bottom temperature in the range from 30 to
100.degree. C., a top temperature in the range from 25 to
50.degree. C. and a pressure in the range from 8 to 15 bar.
The absorption column is preferably a column with random packing or
a column with structured packing. However, any other column is also
conceivable, for example a tray column. A column suitable for the
absorption preferably has 2 to 40 theoretical plates, preferably 5
to 25 theoretical plates.
The temperature of the stream which comprises N-methylpyrrolidone
and water and is supplied to the absorption column is preferably 10
to 70.degree. C., more preferably 20 to 40.degree. C. The
temperature of the stream comprising butene and/or butadiene,
butane, hydrogen and/or nitrogen, with or without carbon dioxide,
is preferably in the range between 0 and 400.degree. C., especially
in the range between 40 and 200.degree. C.
The ratio of N-methylpyrrolidone used to stream comprising butene
and/or butadiene, butane, hydrogen and/or nitrogen, with or without
carbon dioxide, is preferably in the range from 2 to 30, more
preferably in the range from 4 to 30 and especially in the range
from 4 to 15, based in each case on the masses of the streams
used.
The stream which comprises N-methylpyrrolidone, water, butene
and/or butadiene, butane and carbon dioxide, and is obtained in the
absorption, comprises generally 20 to 90 mol % of
N-methylpyrrolidone, 0 to 50 mol % of water, 0 to 20 mol % of
butadiene, 0 to 20 mol % of 1-butene, 0 to 20 mol % of 2-butene, 0
to 50 mol % of butane and 0 to 20 mol % of carbon dioxide.
The stream which comprises N-methylpyrrolidone, water, butene
and/or butadiene, butane and carbon dioxide, and is obtained in the
absorption, is then supplied to an extractive distillation in step
(b).
The extractive distillation can be performed, for example, as
described in Erdol and Kohle-Erdgas-Petrochemie volume 34 (8),
pages 343 to 346 or Ullmanns Enzyklopadie der technischen Chemie,
volume 9, 4th edition 1975, pages 1 to 18.
The extractive distillation is conducted preferably at a bottom
temperature in the range from 100 to 250.degree. C., especially at
a temperature in the range from 110 to 210.degree. C., a top
temperature in the range from 10 to 100.degree. C., especially in
the range from 20 to 70.degree. C. and a pressure in the range from
1 to 15 bar, especially in the range from 3 to 8 bar. The
extractive distillation column preferably has 5 to 70 theoretical
plates.
In the extractive distillation, the stream comprising butene and/or
butadiene, butane, N-methylpyrrolidone, water and carbon dioxide is
contacted with a stream comprising N-methylpyrrolidone and water in
an extractive distillation zone. The extractive distillation zone
is generally configured in the form of a column which has trays,
random packings or structured packings as internals. The extractive
distillation zone has generally 10 to 70 theoretical plates, in
order that a sufficiently good separating effect is achieved. The
extraction column preferably has a rescrubbing zone in the top of
the column. This rescrubbing zone serves for recovery of the
N-methylpyrrolidone present in the gas phase by means of a liquid
hydrocarbon return stream, for which the top fraction is condensed
beforehand. Typical temperatures at the top of the column are
between 30 and 60.degree. C.
The top product stream of the extractive distillation column
comprises butane and carbon dioxide and is drawn off in gaseous
form. In addition to butane and carbon dioxide, it is also possible
for butenes, hydrogen and/or nitrogen and other low boilers to be
present in the top product stream. In a preferred embodiment, the
top product stream is condensed in order to remove CO.sub.2 and any
hydrogen and/or nitrogen and low boilers present from butane. The
liquid butane stream can, for example, be recycled into the
dehydrogenation zone in the case of operation with a
dehydrogenation.
At the bottom of the extractive distillation column, a stream
comprising
N-methylpyrrolidone, water, butene and/or butadiene and butane is
obtained. The stream comprising N-methylpyrrolidone, water,
butadiene and/or butene, with or without butane, which is obtained
at the bottom of the extractive distillation column, is fed to a
distillation column (c) in which butadiene and/or butene and
optionally butane are obtained via the top. At the bottom of the
distillation column, a stream comprising N-methylpyrrolidone and
water is obtained, the composition of the stream comprising
N-methylpyrrolidone and water corresponding to the composition as
added to the absorption and the extraction. The stream comprising
N-methylpyrrolidone and water is divided and passed back into the
absorption and the extractive distillation. The ratio of the
mixture of water and N-methylpyrrolidone which is supplied to the
absorption to the mixture of water and N-methylpyrrolidone which is
supplied to the extractive distillation is preferably in the range
from 0.2 to 20, especially in the range from 0.3 to 15.
The distillation (c) is preferably performed at a bottom
temperature in the range from 100 to 300.degree. C., especially in
the range from 150 to 200.degree. C. and a top temperature in the
range from 0 to 70.degree. C., especially in the range from 10 to
50.degree. C. The pressure in the distillation column 19 is
preferably in the range from 1 to 10 bara. The distillation column
19 has preferably 2 to 30, especially 5 to 20, theoretical
plates.
Alternatively to the withdrawal of the stream comprising butene
and/or butadiene, with or without butane, from the distillation
stage via the top, it is alternatively also possible to withdraw a
butadiene-rich stream as a side draw. In this case, it is possible
to deplete the top stream of butadiene.
A working example of the invention is shown in the figure and is
explained in detail in the description which follows.
A stream 1 comprising butene and/or butadiene, butane, hydrogen
and/or nitrogen, with or without carbon dioxide, is supplied to an
absorption column 3. The addition is effected in the lower region
of the absorption column 3. Via an upper feed 5, a stream
comprising N-methylpyrrolidone and water is added to the absorption
column 3, such that the stream comprising N-methylpyrrolidone and
water, and the stream comprising butene and/or butadiene, butane,
hydrogen and/or nitrogen, with or without carbon dioxide, are
conducted in countercurrent in the absorption column.
The absorption column 3 is operated at a bottom temperature in the
range between 30 and 160.degree. C., preferably in the range
between 30 and 100.degree. C., a top temperature in the range from
5 to 60.degree. C., preferably in the range from 25 to 50.degree.
C. and at a pressure in the range from 2 to 20 bar, preferably in
the range from 8 to 15 bar.
At the top of the absorption column 3 a top stream 7 comprising
hydrogen and/or nitrogen, residues of C.sub.4 hydrocarbons and low
boilers is withdrawn. In one embodiment, a portion of the top
stream 7 is recycled into a butane dehydrogenation from which the
supplied stream comprising butene and/or butadiene, butane,
hydrogen and/or nitrogen, with or without carbon dioxide, may
originate.
At the bottom of the absorption column 3, a bottom stream 9
comprising butene and/or butadiene, butane, N-methylpyrrolidone and
water, with or without carbon dioxide, is drawn off.
The bottom stream 9 is added to extractive distillation column 11
in the lower region. In the upper region of the extractive
distillation column 11, a stream 13 comprising N-methylpyrrolidone
and water is introduced, which has the same composition as the
stream comprising N-methylpyrrolidone and water supplied to the
absorption. The stream 13 comprising N-methylpyrrolidone and water,
and the stream 9 comprising butene and/or butadiene, butane,
N-methylpyrrolidone, water, with or without carbon dioxide, are
likewise conducted in countercurrent.
From the extractive distillation column 11, a stream 15 comprising
butane and carbon dioxide is drawn off via the top. The stream 15
is condensed in a condenser 20. This gives rise to a liquid
butane-rich stream 16 and a vaporous CO.sub.2-rich stream 18. The
butane-rich stream 16 can likewise be recycled into the butane
dehydrogenation.
At the bottom of the extractive distillation column 11 a bottom
stream 17 comprising N-methylpyrrolidone, water, butene and/or
butadiene is withdrawn.
The bottom stream 17 is supplied to a distillation column 19 in
which it is separated into a stream 21 which comprises butene
and/or butadiene and is withdrawn at the top of the distillation
column 19, and a stream 23 which comprises N-methylpyrrolidone and
water and is withdrawn at the bottom of the distillation column
19.
According to the invention, for the absorption and for the
extractive distillation, the solvent used is a stream comprising 80
to 97% by weight of N-methylpyrrolidone and 3 to 20% by weight of
water.
The bottom stream 23 which is withdrawn from the distillation
column 19 and comprises the N-methylpyrrolidone and the water is
cooled in a heat exchanger 27, separated and recycled into the
absorption column 3 or the extractive distillation column 11.
The extractive distillation is preferably conducted at a bottom
temperature in the range from 90 to 250.degree. C., especially at a
temperature in the range from 90 to 210.degree. C., a top
temperature in the range from 10 to 100.degree. C., especially in
the range from 20 to 70.degree. C. and a pressure in the range from
1 to 15 bar, especially in the range from 3 to 8 bar. The
extractive distillation column preferably has 5 to 70 theoretical
plates.
The distillation in the distillation column 19 is preferably
performed at a bottom temperature in the range from 100 to
300.degree. C., especially in the range from 150 to 200.degree. C.
and a top temperature in the range from 0 to 70.degree. C.,
especially in the range from 10 to 50.degree. C. The pressure in
the distillation column 19 is preferably in the range from 1 to 10
bara. The distillation column 19 has preferably 2 to 30, especially
5 to 20, theoretical plates.
EXAMPLES
Example 1
A stream 1 comprising hydrogen, n-butane, butenes and butadiene is
added to an absorption column 3 in the lower region. In the upper
region of the absorption column, N-methylpyrrolidone containing
8.3% by weight of water is introduced as a solvent. At the top of
the column, a top stream 7 comprising hydrogen and butane is
withdrawn. At the bottom, a bottom stream 9 comprising
N-methylpyrrolidone, water, butanes, butenes, butadiene and carbon
dioxide is obtained. The absorption column used is a bubble-cap
tray column with 70 bubble-cap trays having a diameter of 50 mm.
The hydrocarbon feed stream is added above the tenth bubble-cap
tray, and the solvent with a mass flow rate of 16 kg/h above the
60th bubble-cap tray. The inlet temperature of the solvent is
35.degree. C. The absorption is performed at a top temperature of
33.degree. C., a bottom temperature of 51.degree. C. and a pressure
of 10 bara. The mass ratio of solvent to added stream 1 comprising
hydrogen, n-butane, butenes and butadiene is 9.9.
The bottom stream 9 withdrawn from the absorption column is added
to an extractive distillation column 11 as a feed in the lower
region. In the upper region, a solvent comprising
N-methylpyrrolidone and 8.3% by weight of water is added to the
extractive distillation column. At the top of the extractive
distillation column, a top product stream 15 is obtained which
comprises butane and carbon dioxide, and traces of other low
boilers. At the bottom of the extractive distillation column, a
bottom stream 17 comprising N-methylpyrrolidone, water, butanes,
butenes and butadiene is withdrawn. The extractive distillation
column used is a column containing 4.5 m of A3-1000 structured
packing from Montz, divided into 8 packing sections. Above the
structured packing are 14 bubble-cap trays. The bottom stream 9
withdrawn from the absorption column is added above the second
packing section. 20 kg/h of the solvent comprising
N-methylpyrrolidone and 8.3% by weight of water are added above the
eighth packing section and below the bubble-cap trays. The inlet
temperature of stream 13 is 35.degree. C. The extractive
distillation column is operated with a bottom temperature of
139.degree. C., a top temperature of 46.degree. C. and a pressure
of 5 bara. The mass ratio of solvent 5 added to the absorption
column to the solvent 13 added to the extractive distillation
column is 0.8.
The bottom stream from the extractive distillation column is added
as feed to a distillation column 19. In the distillation column, a
top stream 21 comprising n-butane, butenes and butadiene, and a
bottom stream 23 comprising N-methylpyrrolidone and water, are
obtained. The distillation column used is a bubble-cap tray column
having 48 bubble-cap trays. Above the last bubble-cap tray is
installed the column condenser. The bottom stream 17 withdrawn from
the extractive distillation column is added above the thirty-second
bubble-cap tray. The stream 21 is withdrawn as a gaseous
olefin-rich top product. The bottom stream 23 is cooled down to a
temperature of 35.degree. C. in the heat exchanger 27 and recycled
into columns 3 and 11 (streams 5 and 13). The distillation column
19 is operated with a bottom temperature of 163.degree. C., a
temperature below the condenser of 31.degree. C. and a pressure of
3 bara.
The top product stream 15 of the extractive distillation column is
supplied to a condenser 20, and in the condenser a stream 18
comprising essentially carbon dioxide, hydrogen and n-butane, and a
stream 16 comprising essentially n-butane are withdrawn. The stream
comprising essentially n-butane is preferably recycled into a
dehydrogenation for preparation of butenes and butadiene.
The composition and the amounts of the individual streams supplied
or obtained in each case are listed in table 1.
Table 1: Composition of the Streams of a Workup of a
Butene-Comprising Stream from an n-Butane Dehydrogenation in Mol
%
TABLE-US-00001 TABLE 1 Composition of the streams of a workup of a
butene-comprising stream from an n-butane dehydrogenation in mol %
Stream 1 7 15 21 16 18 Hydrogen 32.63 88.43 0.89 0.00 0.00 12.66
Carbon monoxide 0.20 0.61 0.00 0.00 0.00 0.00 Ethane 0.48 0.95 0.31
0.00 0.25 1.34 Ethene 0.03 0.04 0.03 0.00 0.01 0.13 Propane 0.94
1.06 1.62 0.00 1.69 2.14 Propene 0.36 0.06 0.97 0.00 0.94 1.47
Carbon dioxide 3.50 3.86 5.71 0.00 1.74 43.17 Methane 1.55 3.90
0.24 0.00 0.02 3.00 i-Butane 0.13 0.03 0.32 0.00 0.33 0.17 n-Butane
36.24 0.71 84.36 21.89 89.30 33.45 trans-Butene-2 8.84 0.11 0.55
27.27 0.54 0.23 1-Butene 7.18 0.03 4.20 23.59 4.41 1.93 Isobutene
0.10 0.00 0.04 0.27 0.04 0.02 cis-Butene-2 6.73 0.18 0.69 23.15
0.65 0.26 Butadiene 1.09 0.02 0.06 3.82 0.06 0.03 Amount, mol/h
42.46 16.27 13.98 12.21 12.89 1.09
Example 2
A stream 1 comprising hydrogen, nitrogen, oxygen, n-butane, butenes
and butadiene is added to an absorption column 3 in the lower
region. In the upper region of the absorption column, the solvent
introduced is N-methylpyrrolidone containing 8.3% by weight of
water. At the top of the column, a top stream 7 comprising
nitrogen, oxygen, hydrogen and butane is withdrawn. At the bottom,
a bottom stream 9 comprising N-methylpyrrolidone, water, butanes,
butenes, butadiene and carbon dioxide is obtained. The absorption
column used is a column having 20 theoretical plates. The inlet
temperature of the solvent, which is added at a molar flow rate of
9042 kmol/h, is 40.degree. C. The absorption is performed at a top
temperature of 41.degree. C., a bottom temperature of 63.degree. C.
and a pressure of 10 bara. The molar flow ratio of solvent to added
stream 1 comprising hydrogen, nitrogen, n-butane, butenes and
butadiene is 2.7.
The bottom stream 9 withdrawn from the absorption column is added
to an extractive distillation column 11 as a feed in the middle
region. In the upper region, 901 kmol/h of a solvent comprising
N-methylpyrrolidone and 8.3% by weight of water are added to the
extractive distillation column. At the top of the extractive
distillation column, a top product stream 15 is obtained, which
comprises butane and carbon dioxide, and traces of other low
boilers. The return stream at the top of the column is 99.5 kmol/h.
At the bottom of the extractive distillation column, a bottom
stream 17 comprising N-methylpyrrolidone, water, butanes, butenes
and butadiene is withdrawn. The extractive distillation column
comprises 48 theoretical plates. The stream 9 is supplied at the
twenty-ninth theoretical plate, and stream 13 at the forty-sixth
theoretical plate. The inlet temperature of stream 13 is 35.degree.
C. The extractive distillation column is operated with a bottom
temperature of 103.degree. C., a top temperature of 44.degree. C.
and a pressure of 4.8 bara. The mass ratio of solvent 5 added to
the absorption column to the solvent 13 added to the extractive
distillation column is 10.
The bottom stream from the extractive distillation column is added
as feed to a distillation column 19. In the distillation column, a
top stream 21 comprising n-butane, butenes and butadiene, and a
bottom stream 23 comprising N-methylpyrrolidone and water, are
obtained. The distillation column comprises 13 theoretical plates.
The bottom stream 17 withdrawn from the extractive distillation
column is added at the eleventh theoretical plate. The stream 21 is
withdrawn as a gaseous olefin-rich top product. The return stream
at the top of the column is 919 kmol/h. The bottom stream 23 is
cooled in a heat exchanger 27 and recycled to columns 3 and 11
(streams 5 and 13). The distillation column 19 is operated at a
bottom temperature of 171.degree. C., a top temperature of
43.degree. C. and a pressure of 4.7 bara.
The top product stream 15 of the extractive distillation column is
supplied to a condenser 20, and a stream 18 comprising essentially
carbon dioxide, hydrogen and n-butane, and a stream 16 comprising
essentially n-butane, are withdrawn in the condenser. The stream
comprising essentially n-butane is preferably recycled into a
dehydrogenation for preparation of butenes and butadiene.
The composition and the amounts of the individual streams supplied
or obtained in each case are listed in table 2.
TABLE-US-00002 TABLE 2 Composition of the streams of a workup of a
stream comprising butadiene in mol % Stream 1 7 15 21 16 18 Butane
4.56 3.74 85.63 1.20 87.44 23.66 1-Butene 0.02 0.01 0.63 0.00 0.64
0.22 C-2-Butene 0.21 0.06 0.07 1.76 0.07 0.02 T-2-Butene 0.33 0.15
0.75 2.07 0.77 0.21 1,3-Butadiene 9.25 0.01 0.04 93.16 0.04 0.01
H.sub.2O 0.54 0.22 1.86 1.81 1.91 0.17 N- 0.01 0.00 0.00 0.00
Methylpyrrolidone CO.sub.2 1.27 1.19 11.03 0.00 9.13 75.71 O.sub.2
0.02 0.02 H.sub.2 0.04 0.05 N.sub.2 83.77 94.54 Amount, kmol/h 3380
3002 146 330 43 4
TABLE-US-00003 List of reference numerals 1 Stream comprising
butene and/or butadiene, butane, and hydrogen, with or without
carbon dioxide 3 Scrubbing column 5 Stream comprising
N-methylpyrrolidone and water 7 Top stream comprising hydrogen 9
Bottom stream comprising butene and/or butadiene, and scrubbing
liquid, with or without carbon dioxide 11 Extractive distillation
column 13 Stream comprising N-methylpyrrolidone and water 15 Top
stream comprising butane 16 Butane-rich stream 17 Bottom stream
comprising butene and/or butadiene, N-methylpyrrolidone and water,
with or without carbon dioxide 18 Carbon dioxide-rich stream 19
Distillation column 20 Condenser 21 Top stream comprising butene
and/or butadiene and carbon dioxide 23 Bottom stream comprising
N-methylpyrrolidone and water 25 Condenser 27 Heat exchanger
* * * * *